Zombie Panic! Source: ZPO

You will need several ZP:S specific entities to make an objective (zpo) map work properly:

game_win_human game_win_zombie (optional)

You will need to set up an output from the final entity that triggers the end of game, which should look like this:

<output>; game_win_human; end game

Please see the tutorial on creating objectives for a basic list of common objective's used in zpo maps.